This invention relates to hydrodynamic sealing elements of the "washer" style for rotatable shafts, and more particularly to specific geometries or shapes of such elements for use in environments subject to high shaft runout or rotational eccentricity.
Numerous prior art hydrodynamic shaft sealing elements have been employed successfully under a variety of extreme temperatures, pressures, and other environmental conditions. However, in circumstances of severe shaft runout, there have of necessity been compromises in sealability. For example, inert and relatively dense materials such as plastics and polytetrafluoroethylenes have been desirable for assuring superior hydrodynamic sealing quality, durability and resistance to deterioration. In environments of severe shaft runout or eccentricity, however, the sealing elements have typically had to be limited to elastomeric materials for effective sealing due to greater resilience and flexibility of the latter. Thus, in spite of the shortcomings of elastomeric materials in the above-noted respects, they have been relied upon for their high runout followability in the latter environments.
Another aspect of sealing art, beyond the quality or optimal effectiveness of the sealing element per se, relates to achievement of a reasonable useful life of the seal. Of primary concern is the sealability effectiveness of the shaft contact portion of the sealing element. The washer style of sealing element generally has a contact portion about the shaft which defines a band, rather than a ring line as theoretically achieved by a lip style of sealing element. Also, the washer style of element inherently possesses a radially extending flexible body, which when positioned over a shaft for sealing, defines a beam cross-section normally deflected under load. The resulting bending forces are referred to as "beam" forces. Another set of interacting forces are imposed by the normally stretched annulus of mass surrounding the actual contact portion of the washer style seal. The latter are called "hoop" forces, and result from the radially inwardly directed "rubber-band" nature of the sealing lip contact with the shaft. A balance of beam and hoop forces has been difficult to achieve using conventional washer style sealing geometries, and has tended to result in less than a desirable effectiveness for a given sealing requirement. Ideally, sealability of the element would not have to be severely compromised when a relatively dense material, such as polytetrafluoroethylene, is utilized in environments subject to high shaft runout or eccentricity.